My brother, Archie, was diagnosed with the condition in the 1980s, the decade the American Psychiatric Association formally rebranded it “bipolar disorder,” but he was not alone in disliking the newer term, even as it was adopted by his British psychiatrists. He resolutely continued to call himself a manic depressive.

His was a classical case: long periods of raging highs, incarceration in locked wards, abysmal lows. The verbal juxtaposition of manic depression seemed to capture the texture of his experience; “bipolar” sounded tinnily conceptual by comparison.

And if he had a conservative impatience with new-fangled medical terminology, Archie was also comically dismissive of psychological approaches. For him, psychoanalysts were “moonies” and cognitive psychologists were “numpties.” You could say he took an even-handed approach to the factions of psychotherapy. He favored a biomedical model of manic depression — an illness to be treated with medication — because he knew where he stood with that.

He’d be pleasantly surprised to discover that, on one point at least, he has support from the “moony” camp, as represented by psychoanalyst Darian Leader. In this short, essay-length book, Leader picks apart the rebranding and subdividing of bipolar disorder and goes in pursuit of a classical definition of manic depression.

The argument opens on two fronts. Leader attacks the increasing use of bipolarity as a lifestyle term: a cultural shift from the fad for depression of the 1980s to a more recent fascination with mood swings and the “creativity” of mania, as evoked by Claire Danes in “Homeland,” or Bradley Cooper in “Silver Linings Playbook.” He blames the forces of pop culture and pharmaceutical marketing for turning a categorical psychiatric concept into a dimension of symptoms: a mood spectrum wide enough to encompass almost anyone who experiences highs and lows.

Leader also lays the blame at the doorstep of American psychiatry. Between the third edition of the “Diagnostic and Statistical Manual of Mental Disorders,” published in 1980, and the fifth edition, published this year, diagnostic subdivisions have proliferated, allowing for bipolars 1, 2, 3 and so on. This has had a far greater impact on American rates of diagnosis than it has had on British ones (and it’s a pity that Leader tends to conflate the two cultures), but the general point is well made. When a diagnosis seeks to be both categorical and dimensional — at once a disease and a spectrum of symptoms — it loses the power of definition.

So what is manic depression? Leader initially advocates the approach of the 19th-century French psychiatrists Jean-Pierre Falret and Jules Baillarger, who first defined “double form madness,” while dismissing the ideas of the German Emile Kraepelin, who viewed combined mania and melancholia as belonging to the same disease. Leader makes a significant gesture in starting prior to Freud, suggesting that this is not mere psychoanalytic theory. But he is really using Falret and Baillarger to undermine Kraepelin’s biological explanation so that he can define manic depression as, principally, a system of thought.

When describing particular case histories — either those of his own patients, or those to be found in the memoirs of well-known sufferers — Leader’s psychoanalytic skills are elegantly deployed. His descriptions of manic depressive behavior and thought patterns, along with his ability to interpret these for individuals, make a powerful statement of the importance of understanding the psychology of even the most floridly psychotic patient.

Leader notices interesting manic depressive traits: nonviolence in sufferers who otherwise appear to be raging, a curious empathy and generosity, social and verbal dexterity in mania and a concomitant disintegration in the ensuing depression. He rightly argues that the precise meaning of personal histories (as provided by famous cases, such as those of Stephen Fry and Kay Redfield Jamison) need interpretation. I recognize a depth of psychological understanding here that was lacking, perhaps crucially, from my brother’s early treatment.

But as Jamison, author of the classic memoir “An Unquiet Mind,” wrote: “People go mad in idiosyncratic ways.” While Leader is good on the idiosyncrasies, he is terrible at the universals. Attempting to define the “latent motifs” of manic depression, he seeks increasingly garbled explanations in tropes of language and symbolism. One result of this is to miss the self-evident physiological features of cases like my brother’s, whose manic episodes were triggered by cannabis use. This is not to suggest that neurochemical components are the sole explanations; but to ignore elementary medical facts in favor solely of personal meaning is as blind as believing that psychology is irrelevant.

Even on his own terms, Leader’s grand definition of manic depression falls into incoherence. The case he refers to most often in this essay is that of Stephen Fry. Fry, though he has produced interesting films and memoirs about manic depression, has conceded that his is not the more acute form of the illness. He has described himself as “bipolar lite,” and Leader fails to note that one of his key case histories belongs to exactly the kind of spectrum disorder that he attacks.

Though he yearns for authoritative definition, the language of Leader’s profession — psychoanalysis — is precisely an exploration of the dimensions of human meaning. That’s what it’s good at.

It is the purpose of medicine, meanwhile, to identify categories of illness. This is nowhere more philosophically difficult than it is in psychiatry. But if illnesses of the mind exist, medical science has to define the essentials, rather than merely proliferating and subdividing terms. If psychiatry can’t do this rigorously, we might as well fall in with the magazine headline: “We’re all bipolar now.”